Instrumental and Perceptual Evaluation of Voice Quality in Multiple Sclerosis Patients Treated with Deep Brain Stimulation for Intention Tremor and Upper Limb Ataxia

Objectives: The effect of deep brain stimulation (DBS) on voice quality in 8 patients with multiple sclerosis (MS) was examined instrumentally and perceptually. Methods: First, vowel productions of the patients (produced with and without stimulation) and of a group of 16 healthy control speakers were analysed. Second, the acoustic signals of the same vowel productions were prepared for perceptual evaluation. Results: With stimulation, phonation has a greater tendency to be strained and, in comparison to the healthy control data, hyperfunctional phonation behaviour can be identified under this condition. The results of perceptual evaluation support this strained phonation behaviour under stimulation resulting in a smaller degree of breathiness ratings of all raters. Without stimulation, a higher rate of perturbation in the acoustic signal can be shown. These findings are also supported in the perceptual experiment providing a higher degree of roughness ratings of all raters for these signals. Conclusion: The results suggest the need for long-term monitoring of phonation behaviour during DBS in order to initiate adequate treatments without delay.